If one remembers a document, but not the app which was used to create it, it’s hard to find it again, as the system-wide search in iOS cannot search in third-party apps (at least it couldn’t when this feature was released in iPhone OS 3.0, and I am not aware of this having changed), so one has to search each and every app where this document could have been made.
In some cases, for a project for instance, it is necessary to group documents created by different apps: sometimes there is no single app that can manage all the different media for a single project. On iOS these documents can only exist segregated into their own apps with no way to logically group them.
Organizing documents based on their app is akin to organizing notes based on the pencil you used to write them.1
The most extraordinary invention would have to be the digital canvas. A weave not of components, but of some sort of primordial ooze. Something that would have digital natural laws, on top of which you could build new things and reuse it for completely unintended purposes.
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